1. Technical Field
The present invention relates to a projector.
2. Related Art
There is a known projector of related art that modulates a light flux outputted from a light source apparatus in accordance with image information and projects the modulated light flux through a projection lens. Further, there is a projector in which a projection lens including a reflective optical element reflects and projects such a modulated light flux on a screen or any other surface.
JP-A-10-133101 discloses a projection apparatus that performs projection with the exiting angle of light that exits out of a projection optical system inclined to a base surface to correct distortion, trapezoidal distortion, image plane inclination, and other defects of projected video images. JP-A-2005-301074 discloses an optical system for correcting video images by using inclination created by a mirror, which is a reflective optical element.
FIG. 7 is a diagrammatic view showing a case where a projector 900, to which a reflective projection lens 910 of related art is attached, is used to project an image on a screen SC.
When the reflective projection lens 910 including a reflective optical element 911 is used to project an image on the screen SC, the projected image typically tends to have an image plane C that is curved (field curvature) or does not coincide with a flat surface A of the screen C, as shown in FIG. 7. In FIG. 7, the reflective optical element 911 includes a convex lens, which causes the image plane C to be concave toward the reflective optical element 911. Specifically, an image portion projected on a lower portion of the screen SC (portion closer to installed projector) is brought into focus, but an image portion brought into focus shifts forward away from the screen with distance upward from the lower portion because the image plane is curved.
A user who looks at the image projected on the screen SC can recognize a clear, focused image in the lower portion of the screen SC. However, the user recognizes a blurred image in an upper portion of the screen SC, and the degree of the blur increases with distance upward from the lower portion or with distance from the lower portion toward the periphery (corners in particular) of the screen SC. To avoid the phenomenon of what is called field curvature or to correct the projected image, the reflective optical element 911 in the projection lens 910 is designed, for example, to have an aspheric surface or a free-form surface.
Correcting the field curvature by designing the reflective optical element, for example, to have an aspheric surface or a free-form surface, however, requires changing the curvature of the surface of the reflective optical element in a complicated manner, undesirably resulting in complicated design and hence an increase in design burden. Further, since the surface shape is complicated, manufacture of the reflective optical element undesirably requires high-precision surface processing. Moreover, the reflective optical element undesirably tends to have a large aperture diameter (projection lens tends to have large outer shape).
It is therefore desired to provide a projector capable of lowering the degree of field curvature when a projection lens including a reflective optical element is attached to the projector.